Ignition device for high-power arc lamps



ul 31, 1934. a V H E K 1,968,011 mnn'ion DEVICE FOR HIGH VPOIER ARC miPs Fiiea Opt. 20. 1931 v lm'e'niar';

Patented July 31, 1934" UNITED STATES IGNITION DEVICE FOR HIGH-POWER ARC LAMPS Heinrich Beck, Meiningen, Germany, assignor to v firm Carl Zeiss, Jena, Germany Application October 20, 1931, Serial No. 569,954 In Germany ctobcr 23, 1930 i o aims. (01. 176-55) I have filed an application in Germany, October 23, 1930.

High-power arc lamps of the kind specially used m search lights have been ignited in the manner common with are lamps, namely by making the electrode tips touch each other and part.

However, with arc lamps of specially high intensities, viz. 200 to 500 amperes and more, this kind of ignition entails certain disadvantages. When the carbon ends touch each other the current rises too far above the normal strength and assumes high values. Moreover, recesses are in most cases burnt into the carbons when they are intouch with each other, which means that the crater surfaces have to suffer an undesirable deformation. Another drawback is that the carbon ends may splinter. disadvantage which consists therein thatthe usual ignition device hardly permits of efiecting the ignition within a very short time. The ever increasing demands upon high-power search lights, especially upon those for military purposes, require ignition periods ranging down to 0.1 second, the chief requirement being that during the working of the search light any rupture of the light are, which may be caused for instance by shooting oil a heavy gun or by a detonation, is succeeded so quickly by the re-ignition that any interruption of the light is hardly noticeable. With arc lamps of very strong currents any rapid ignition is possible only with great difficulty. In lamps of this kind the carbon as well as the carbon holder are rather heavy, which, to-

gether with purely mechanical reasons, makes it I diflicult to effect the reciprocating movements for the ignition within a short period. Greater difliculties are encountered when the electrodes are guided in electrode heads. -In this case also the heavy electrode head must be moved .to and fro, which means that the above mentioned disadvantage is even more pronounced, or the electrode is to be displaced in the carbon holder. However, when displacing the carbon holder, a considerable friction must be overcome, which is due to the necessary contact pressure, this friction representing a special difiioulty with respect to quick ignition movements.

The present invention overcomes all these disadvantages by using a special auxiliary ignition electrode and by giving the current in the ignition circuit such a strength that removing the ignition,

electrode from the negative main electrode causes the arc to jump by itself to the positive main electrode without the ignition electrode touching this main electrode. I

There is still a further The accompanyingdrawing represents in front elevation, partly in a section, a constructional example of an ignition device according to the invention. a

The positive and the negative electrode of the lamp and the ignition electrode are designated a, b, and 0, respectively. The ignition electrode 0 moves easily in a guide d and is fixed to a lever system c connected by means of a lever f tothe armature f of an electro-magnet f which a tension spring I gives the position represented in the drawing. At its one end the lever f is fixed to a piston g which fits narrowly into and emerges in a dash-pot 9 having below an aperture o The ignition electrode 0 is connected by means 7 of a lead c to the positive supply lead of the lamp. Between this positive lead and the ignition electrode is connected a current limiting resistance 0 When in this device the lamp is switched on, the magnet ,f attracts its armature f and the Z 5 ignition electrode 0 is taken away from the negative electrode b, a light are being formed which, when the current in the ignition circuit is strong enough, at once jumps over to the positive main electrode a without the ignition electrode touching this main electrode. When the armature f reassumes its original position, the movement of the ignition electrode is strongly damped towards its end by the piston g, the ignition electrode thus being prevented from striking too strongly against the negative electrode b.

With the lamps according to the invention the ignition light are is not required to be of the length of the main are, an ignition already taking place when the light are is only a few millimeters long. Apparently this phenomenon is due to the fact that, when the current is sufliciently strong, the negative electrode repels the electrons (also when covered with substance) in a cathode-ray like manner at right angles to the surface, regardless of the position of the auxiliary anode. These electrons strike the main anode, and the ignition is effected immediately. This ignition process is therefore not to be compared either with those caused by the known ignition devices in arc lamps'of the usual weak currents, in which it has been tried to make the light are ignite by drawing it to the positive carbon by means of an auxiliary electrode, or with devices in which an ignition .rod is made to lie between carbons, thus causing them to be shortcircuited, and effects the ignition by combining the two arising light arcs. With the first said device the ignition is caused by the auxiliary ig-,- nition are being elongated until the light are 11 flows round the main anode and partakes of the conduction of current. -In this case the auxiliary ignition arc must be formed comparatively slowly as, otherwise, it would break without reaching the length required for the ignition.

' order to reach the anode with suificient speed. By

way of example there may be remarked that with a definite carbon material and a space of 37 millimeters between the electrodes the strength of current of the ignition light are with which the novel phenomenon still could be noticed, amounted to approximately 40 amperea, v Above this value the phenomenon appeared always,'-below this value the ignition became rather uncertain and finally ceased altogether.

The strength of the ignition current can be adjusted to the desired degree by means of a resistance. This resistance-may be dispensed with if the thin ignition electrode, which may be of carbon, metal or anyother conductive material, oifers a sufficient resistance. The current of the ignition light arc is generally given a strength not surpassing the normal strength of the lamp current, which is in general considerably higher than the above mentioned lowest strength of the ignition current. As will be explained further below, the new device permits to attain extraordinarily short ignition periods, and for this reason it is possible to reduce the impulse of the ignition current to the desired degree by using of the lamp current. The dangerous impulse of the ignition current, which, with a lamp of for instance 450 amperes and the kind of ignition used hitherto, is caused by the touching of the -two electrodes and may amount to one and a half and more of the normal strength of ourrent, is therefore completely'eliminated in the new device. Moreover, the positive crater never can be damaged by electrode contact. Also any deformation of the negative crater is not to be feared, since with a lamp of for instance 450 amthis carbon very thin and consequently light.

For the same reason specially strong current supply leads are not required. Further, the carbon can move easily in its guides. The light weight of the carbon and its mobility permit to move the ignition carbon exceedingly quickly, and the ignition periods can be reduced to 0.2 to 0.1 sec- 0nd. Such short ignition periods make it hardly possible to perceive any rupture of the light arc,

fluctuation of light.

tion without the auxiliary electrode touching the such rupture being perceptible only by a slight The new ignition device even permits to eventually burn the search light without a cover glass, since in the case of the influence of the wind breaking the light arc the re-ignition is eifected so quickly that hardly any interruption is noticed; 'Such short ignition periods requiring the ignition carbon to move extraordinarily quickly, special means have to be provided in order to prevent the said carbon from striking too strongly against the main electrode. For this reason, as mentioned already, the speed of the ignition carbon is strongly reduced immediately before this carbon strikes against the electrode. This can be effected in different manners. If the ignition carbon is moved by means of a magnet, the reduction of speed can be effected for instance in the way suggested by the drawing, viz. by means of a dash pot. If the ignition carbon is moved by means of an electric motor, its speed can be suddenly reduced by a short-circuit brake, &c.

The position of the ignition carbon is in general of no importance, since an ignition takes place in nearly any position of this carbon. 10 However, with a view to avoid anyundesirable additional losses of light, the ignition carbon is conveniently given in search lights such a position that this carbon as well as the levers are in the shade as far as possible.

I claim:

1. In a high-power arc lamp, an anode, a cathode, and a third, auxiliary, electrode, the auxiliary electrode being movable and so disposed that it can touch the cathode only, and means bringing the auxiliary electrode in and out of contact with the cathode, a resistance in the circuit to which the anode and the auxiliary electrode are connected which is so high that withdrawing the auxiliary electrode from the cathode gives rise L to a light arc between the auxiliary electrode and the cathode, this light are having such strength that the negative flame emanating from the cathode reaches the anode and causes the ignition without the auxiliary electrode touching the anode.

2. In a high-power arc lamp, an anode, a cath ode, and a third, auxiliary, electrode, the auxiliary electrode being movable and so disposed that it can touch the cathode only, andmeans bringing the auxiliary electrode in and out of contact with the cathode, a resistance in the circuit to which the anode and the auxiliary electrode are connected which is so high that withdrawing the auxiliary electrode from the cathode gives rise to a light arc between the auxiliary electrode and the cathode, this light are having such strength that the negative flame emanating from the cathode reaches the anode and causes the ignianode, the resistance. and the self-induction in posed in the space below the anode and the cathode.

HEINRICH BECK. 

